1. Technical Field
The present invention relates to a drive circuit of an electro-optical device such as a liquid crystal display, a driving method of the electro-optical device, and an electro-optical device having the drive circuit.
2. Related Art
A liquid crystal display is an example of an electro-optical device. An inversion driving method such as a dot inversion type, a line inversion type, and a surface inversion type is employed for driving the liquid crystal display. The respective inversion driving methods have advantages and disadvantages. The dot inversion type or the line inversion type has an advantage that crosstalk can be suppressed, but has a disadvantage that since potentials with inverse polarities are applied to neighboring pixel electrodes, a transverse electric field is generated between neighboring pixels. Since the transverse electric filed disturbs the alignment of liquid crystal molecules and thus causes the leakage of light, the transverse electric field is an important factor for deterioration in display quality such as decrease in contrast ratio or decrease in aperture ratio. Accordingly, in the future tendency of decrease in pitch, the surface-inversion type driving method little affected by the transverse electric field is advantageous.
On the other hand, the surface-conversion type driving method has another disadvantage. That is, in the surface inversion type, since positive-polarity fields (or positive-polarity frames) and negative-polarity fields (or negative-polarity frames) are asymmetrical regardless of the magnitude of an applied voltage with intermediate potentials, a flicker with a field cycle (or a frame cycle) occurs. In addition, paying attention to any one data line, if a cycle of inverting polarities is one field in all the pixels to be supplied with signals from the corresponding data line, image signals with the same polarity are written in a predetermined field. Then, in the next field, the polarity of the image signals to be supplied to the corresponding data line is inverted. At this time, since a display area is scanned from the upside to the downside, the polarity of the image signals to be supplied to the data line is equal to that of a sustained signal potential during a most sustain period after having written the image signals in the upper pixel side of the display area. On the contrary, the image signals with the polarity opposite to that of the sustained signal potential are supplied to the data line during the most sustain period after having written the image signals in the lower pixel side. In this way, when the upper pixel side and the lower pixel side of the display area are different in influence of the potential of the data line on pixel electrodes, electric charges may be leaked from the pixels at one side of the display area, thereby not accomplishing a proper display. For example, display brightness may be vertically deviated or a black image may seem to have a shadow.
In order to secure uniformity in image quality, for example, there has been suggested a technique, which is disclosed in JP-A-5-313608, that one horizontal scanning period is divided into a first period and a second period, image signals are applied to pixel electrodes by supplying driving pulses to the scanning lines and supplying the image signals to the data lines in the first period, and the image signals with the polarity opposite to the previous polarity are supplied to the data lines without supplying the driving pulses to the scanning lines in the second period.
Such studies for temporarily and spatially reducing display noises occurring during operation have been made in other inversion types other than the surface inversion type. For example, a driving method is disclosed in JP-A-10-253939, in which a scanning speed is increased to double, the same image signals are written to two lines while inverting the image signals in the same polarity pattern in a horizontal scanning period, and the writing lines is changed line by line every field, for interpolation of signals when interlace signals of an NTSC method, etc. are displayed in a non-interlace manner. In the technique, since DC components remain in the pixel portions due to the writing of the image signals with the same polarity to the same line in two neighboring fields, the polarity inversion pattern is further controlled to reduce the display noises due to the DC components.
However, the technique disclosed in JP-A-5-313608 has a disadvantage in that the time usable for the writing operation is reduced to half a normal time and thus the writing operation is not sufficiently carried out. In addition, in the technique disclosed in JP-A-10-253939, the flicker, etc. can be made to be invisible, but another study is required to reduce the noise components and thus to radically improve the display quality. The above-mentioned disadvantages are not limited to the liquid crystal display, but may be fundamentally caused in any electro-optical device employing the polarity-inversion driving method.